Corrosion inhibition of metal surfaces by aromatic aldehydes



3,453,203 CORROSION INHIBITION OF METAL SURFACES BY AROMATI'C ALDEHYDES Zisis Andrew Foroulis, Morristown, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware N Drawing. Filed Apr. 8, 1966, Ser. No. 541,136 Int. Cl. C23g 1/06; C10g US. Cl. 20847 9 Claims ABSTRACT OF THE DISCLOSURE Corrosion of metal surfaces, and particularly carbon steel by acids in petroleum process equipment having an inert atmosphere is inhibited by introducing an aromatic aldehyde into the system. Benzadehyde and naphthaldehyde are suitable aldehydes.

This case relates to the inhibition of corrosion. More particularly, the case relates to the inhibition of corrosion in an inert atmosphere. That is to say, corrosion which takes place in the absence of oxygen. The corrosion is prevented by adding an aromatic aldehyde to the system in which the corrosion is taking place. Suitable aldehydes for this purpose include benzaldehyde and naphthaldehyde as well as derivatives thereof. The advantages of using the aforementioned aldehydes are numerous; they include maximum protection from corrosion without any deleterious effects on catalytic systems with which they may come in contact.

It is well known that various organic and inorganic materials cause extensive damages to any metallic surfaces with which they come in contact. Examples of especially destructive inorganic compounds include HCl, H 8 and H 80 With respect to organic compounds, acetic acid, phenolic solutions and naphthenic acids are extremely troublesome. The various organic chlorides also tend to be quite corrosive; they usually do not occur naturally in crude oil but are sometimes added by producers for removal of parafiin deposits in producing wells and pipelines. Generally, these corrosive materials fall within the definition of a Bronsted acid. A Bronsted acid is defined as any substance that can lose one or more protons.

In particular, the petroleum industry has suffered greatly in loss of equipment and time because of the presence of the various corrosion-causing compounds. Most crude petroleums contain numerous naturally occurring constituents and impurities which will cause severe corrosion of the meals from which conventional petroleum refinery equipment is constructed. This is, of course, predominantly carbon steel. 7 In the past, it has been known to use various inhibitors in order to prevent this corrosion. For instance, benzaldehyde, in the presence of oxygen, is oxidized to benzoic acid. Consequently, to rid a system of oxygen, which is a particularly corrosive material, one would add benzaldeyhde and remove the oxygen by utilizing it to oxidize the benzaldehyde to benzoic acid. The benzoic acid, which is highly insoluble, would be precipitated out of the solution. Various other alternatives for the removal of corrosion-causing materials in the presence of oxygen are well known. However, the problem of corrosion in an inert atmosphere, i.e., in the absence of oxygen, is another matter entirely. This problem remains substantially unsolved, particularly when catalytic systems are present since most corrosion inhibitors tend to deactivate catalysts.

According to this invention, it has unexpectedly been discovered that the addition of an aromatic aldehyde such as benzaldehyde, naphthaldehyde or derivatives thereof, in an inert atmosphere, serves to prevent the corrosive effects of the various known corrosive agents on various metallic surfaces. The corrosive effects of highly corrosive agents such as H S, HCl, other chlorides both organic and inorganic and H will be successfully inhibited. Generally, the acids which may be inhibited by the instant invention include the organic acids such as acetic acid, naphthenic acid, organic acid halides, non-aqueous solutions such as formamide, dimethyl-sulfoxide, etc. The various inorganic acids are also corrosive and the presence of the inhibitors of the instant invention also serves to inhibit metal corrosion caused by these inorganic acids. Examples of these inorganic acids include hydrochloric acid, sulfuric acid, dilute nitric acid, sulfurous acid, hydrofluoric acid, fumaric acid, citric aid, succinic acid, dilute perchloric acid, polyphosphoric acid, etc.

The metals which may be protected from corrosion by the process of the instant invention include carbon steel, nickel steel, copper and its alloys, stainless steels, etc. However, it should be emphasized that this invention will be most useful in preventing the corrosion of carbon steel, particularly as used in petroleum refinery facilities.

Since this invention is to be utilized in an inert atmosphere, i.e., in an atmosphere in which oxygen is present only in trace amounts if at all, its prime use will be in the areas where chemical reactions or physical change is brought about in an inert atmosphere such as nitrogen, hydrogen, C0, C0 N containing small amounts of S0 S0 or mixtures of these various inert gases. An inert atmosphere is found frequently during the regeneraion of catalysts for hydroforming and hydrotreating or other catalytic hydrogenation processes. It is an important part of this invention that in all instances where the corrosion is prevented no significant deleterious effect on any catalyst with which the aromatic aldehyde, i.e., benzaldehyde, naphthaldehyde or derivatives thereof come in contact is observed. This is particularly important in the case of hydroforming and hydrotreating where the catalysts are expensive and it is extremely crucial to extend their life for as long a period as possible.

Hydroforming is now a matter of record and commercial practice in this country. Basically, the operation involves the contacting of a naphtha, either virgin, cracked, Fischer-Tropsch of any mixture thereof, with a solid catalytic material. The catalyst usually includes platinum or palladium dispersed upon alumina. Catalytic material is contacted with the feedstock at elevated temperatures and pressures in the presence of added hydrogen.

The reactions involved in hydroforming are: (1) dehydrogenation of naphthenes to the corresponding aromatic hydrocarbons as where methylcyclohexane is dehydrogenated to form toluene; (2) isomerization of paraflin to form branched-chain paraflins or isomerization of ring compounds, such as ethylcyclopentane to form methylcyclohexane, which latter compound is then dehydrogenated to form toluene: (3) dehydrocycloization of parafiins to aromatics such as n-heptane to form toluene; and (4) hydrocracking of the higher boiling constituents of the feed to form lower boiling constituents.

As indicated above, catalysts that may be used for hydroforming a feedstock are those containing 0.01 to 1.0 wt. percent platinum or 0.1 to 2.0 wt. percent palladium dispersed upon a highly pure alumina support such as is obtained from aluminum alcoholate, as per US. Patent No. 2,636,865, or from an alumina hydrosol prepared by bydrolyzing aluminum metal with dilute acidic acid in the resence of very small catalytic amounts of mercury. A uitable catalyst comprises about 0.2 to 0.8 wt. percent platnum widely dispersed upon alumina in the eta or gamma )hase derived from a suitable aluminum alcoholate and Jetween about 0.3 and 1.2 wt. percent chloride and having L surface area of about 50 to 300 square meters per gram. I-Iowever, a variety of other catalysts may be utilized such is platinum on desurfaced silica-alumina.

Regeneration occurs at least once a month for each hylroforming reactor depending upon the feed quality and feed severity. However, in many cases more frequent regeneration is required. During regeneration coke is burned from the catalyst producing an environment which has a fair concentration of CO and small quantities of S and 30 During this step, the chlorides to be found in the gas phase will increase due to an increase in water content of the gas which serves to strip the chlorine off the catalyst. The second step is to remove any water left on the catalyst. This means thorough drying of the flue gas, which is a mixture of nitrogen, CO CO, S0 S0 and HCl. After most of the Water has been removed, chlorination is started in a manner such that chlorine will be progressively absorbed by the catalyst. During the subsequent rejuvenation of the catalyst to rearrange the crystal structure, some chlorine will still be carried over with the flue gas. The last step in the regeneration operation is purging the system with nitrogen, an inert gas, to remove air and finally pressure up with hydrogen. It is after purging that the inhibitor of the instant invention is injected in the system to prevent its possible oxidation by air at the high temperatures. The presence of the inhibitor serves to reduce or minimize corrosion in heat exchanging equipment and transfer lines where Water condensate, containing the acidic components mentioned previously, accumulates. The inhibitor compound adsorbs on the metal surface and minimizes corrosion by markedly lowering the rate of the corrosion reactions. As indicated earlier, the presence of naphthaldehyde, benzaldehyde and derivatives thereof, in the absence of oxygen, serves to inhibit the corrosive effects of various corrosion causing materials on metals. Here, in the case of hydroforming, an inert gas atmosphere is present, nitrogen, and in addition, corrosives such as H 8, HCl and H 50 are present. The addition of an aromatic aldehyde such as naphthaldehyde, benzaldehyde or derivatives thereof serves to minimize corrosion with no adverse efiect on the platinum or palladium catalyst. Naphthaldehyde and derivatives thereof is preferred for use in inhibiting corrosion in hydroformers.

Another area where corrosion in an inert gas atmosphere is very wide spread and has a most deleterious effect is in hydrotreating. Briefly, hydrotreating involves three main sets of reactions. Initially, there is sulfur reduction; sulfur in the form of mercaptan, disulfide or thiophene is reduced. In addition, oxygen is removed from various compounds such as phenol and peroxide. Olefins are saturated and form the corresponding paraffin. All of these reactions require the presence and consumption of hydrogen. These reactions may take place in the presence of a variety of catalysts; perhaps, the most Widely used is cobalt molybdate. A great problem in hydrotreating is the presence of organic chlorides such as carbon tetrachloride and trichloroethylene. In addition, HCl i often found within the hydrotreater; the original source of this HCl may be organic chloride or hydroformer treat gas. In any event, the hydrotreater efiluent condenser and other overhead equipment has been plagued with corrosion problems instigated by the presence of hydrogen chloride. In addition, as would be expected a great deal of H 8 is produced when sulfur is reduced in the hydrotreater. This causes severe corrosion particularly in the presence of water condensate. The effluent stream in the hydrotreater is predominantly hydrogen gas which is inert and water vapors, HCl and H 5. The addition of benzaledehyde or naphthaldehyde or derivatives of either to this effluent stream serves to inhibit the corrosion. Once again it should be emphasized that substantially no oxygen is present and any oxygen which is present is detrimental to the effective inhibition of corrosion. Additionally, no effect is expected upon the catalyst by the presence of naphthaldehyde or benzaldehyde or derivatives thereof. In a hydrotreating operation, it is preferred to use benzaldehyde because of the lower cost of benzaldehyde. All hydrotreating reactions may be improved by the instant process; thi would include the Unifining operation sponsored jointly by Union Oil Company and UOP, the Trickle Process of the Shell Oil Company and Esso Researchs Hydrofining Process.

It is absolutely critical to the process of the instant invention that the compound added have an aldehyde grouping attached to a benzene ring. The preferred additives of the instant invention are benzaldehyde and naphthaldehyde. Benzaldehyde has a single aromatic ring and naphthaldehyde has two condensed aromatic rings. Both compounds, of course, have an aldehyde grouping joined to the aromatic ring. Suitable derivatives which may be used with the process of the instant invention are quite varied in scope. Thus, a third aromatic ring may be added so long as there is an aldehyde grouping joined directly to an aromatic ring. In addition, other substitutions may be made in the benzene ring of benzaldehyde or the rings of naphthaldehyde. Thus, a C -C alkyl group may be added to any carbon on the benzene ring; a hydroxyl group may also be added to any of the carbons of the benzene ring. It is preferred to add an alkyl group or a hydroxyl group to no more than one member of the benzene ring. It is preferably the alkyl or hydroxyl group to be added to the benzene ring not be directly attached to the aldehyde group.

The concentration of benzaldehyde, naphthaldehyde or derivatives thereof may vary widely depending upon the particular corrosive solution and the pH of the solution. For a corrosive solution of pH of 0 to 1, 10 to 12,000 parts per million, preferably 50 to 1000 parts per million of inhibitor should be added. When the corrosive solution has a pH of 1 to 4, about 10 to 1000 parts per million of the corrosion inhibitor of the instant invention should be added, most preferably 30 to 400 parts per million. The naphthaldehyde, benzaldehyde and derivatives thereof may be added directly into the vapor or liquid stream. In the case of the hydroforming process, the inhibitor should be injected directly in the vapor stream in the outlet of the hydroforming reactor. In the case of hydrotreating the inhibitor again should be injected directly in the vapor stream in the outlet of the hydrotreating reactor.

The following explanation is offered for the effectiveness of the instant invention. There is no intention to be bound by any particular mechanism and the mechanism offered is just for purposes of clarity. The additive, naphthaldehyde, benzaldehyde or derivatives thereof, is adsorbed on the metal surface and serves to insulate the metal from the corrosive material. There is substantially no chemical change effected in the additive within the corrosive solution since an inert atmosphere is maintained over the corrosive solution.

The additive of the instant invention may be used in extremely broad temperature ranges. Benzaldehyde, naphthaldehyde or derivatives thereof would effectively inhibit COI'I'OSIOH at temperatures of 40 to 212 F., preferably 40 to 200 F. and in its most preferred range this additive would be used at a temperature of 70 to 180 F. The pressure range is also quite broad and pressures of 14 p.s.i. to 200 psi. may be utilized in conjunction with this invention. Pressure is not critical since the invention may be utilized with the additive in both the liquid and vapor phase. Contacting times for the additive with the corrosive solution may vary widely; effective times between 0.1 and 2 minutes may be effectively utilized.

It is extremely important that the additive of the instant invention be utilized in an inert gas atmosphere. That is to say, an atmosphere in which oxygen, if present at all, is not found in greater amounts than 0.5 to 1% by weight Broad range --10- Preferred range 10 5 10- Most preferred range 10 -10 Example 1 This example illustrates the ability of benzaldehyde to control the corrosion of 1020 carbon steel which contains 0.2% carbon. Carbon steel is injected in 0.1 N/HCl (pH equals 1.0). A glass reaction container was used for the experiments; the atmosphere within the vessel was substantially all nitrogen.

TABLE IIL-PROTECTIVE PROPERTIES OF NAPHTHYL- ALDEHYDE TO CONTROL CORROSION OF 1020 CARBON STEEL IN 0.1 N HCl (pH=1. 0) AT C.

Corrosion ate (mdd.) Percent Inhibitor Concentration (Moles of Inhibj mgn/dmfi/ Inhibitor Liter of Solution) day Efliciency Blank 1,555 a-Naphthylaldehyde 5Xl0- M/L 747 52. 0 a-Naphthylaldehyde 1Xl0- M/l- 7. 5 95. 5 fl-Naphtliylaldehyde 1Xl0- M/l 1, 190 23. 5 fi-Naphthylaldehyde 5X10- M/l 176 88. 7 fl-Naphthylaldehyde 1X10 M/l 11 99. 3 B-Naphtliylaldehyde 1X 10' M/l 2. 4 99. 8

The above table, Table III, demonstrates the corrosion inhibition in an atmosphere of nitrogen of 1020 carbon steel immersed in 0.1 N HCl. The apparatus used was a glass container. This data indicates once again that the percent inhibitor efliciency increases as the concentration of inhibitor approaches l 10 mols per liter. It also indicates that B-naphthylaldehyde is a better inhibitor, under identical conditions, than a-naphthylaldehyde.

TABLE IV.PROTECTIVE PROPERTIES OF NAPHTHYLALDEHYDES TO CONTROL CORROSION OF 1020 CARBON STEEL IN HCl Concen- Inhibitor Concentration (M/l.) Corrosion Percent tration ates Inhibitor of HCl (mdd.) Efliciency an fi-Naphthylaldehyde 10- M/l" TABLE I.-PROTECTIVE PROPERTIES OF BENZALDE- HYDE TO CONTROL CORROSION OF 1020 CARBON STEEL IN 0.1 N HCl (pH=1.0), 25 C.

The above table, Table I, indicates that benzaldehyde is an efficient corrosion inhibitor. The efiiciency of the benzaldehyde increases as the concentration approaches 1 10 mols per liter; at this level the inhibitor efiiciency is 97.4% as compared to 13.1% for a l0 M/l. concentration.

The above table, Table IV, demonstrates the percent of inhibitor efficiency of naphthylaldehyde at a concentration of 10 mols per liter. The varying of temperatures, as well as concentrations of HCl did not bring about any more than a minor decrease in the percent of inhibitor efficiency.

Although this invention has been described with some degree of particularity, it is intended only to be limited by the attached claims.

What is claimed is:

1. A process for inhibiting corrosion of metallic vessels by an aqueous hydrochloric acid solution in a reaction system having a vapor phase therein, which consists essentially of adding to the system at least one aromatic aldehyde and thereby substantially inhibiting said corro- SlOIl.

TABLE II.PROTECTIVE PROPERTIES OF BENZALDEHYDE TO CON- TROL CORROSION OF 1200 CARBON STEEL IN HCl Example 2 In this example, the relative corrosion inhibition of the various naphthaldehydes is demonstrated in an atmosphere of nitrogen.

2. The process of claim 1 in which the aldehyde is benzaldehyde, naphthaldehyde, or a derivative thereof.

3. The process of claim 1 in which the aldehyde is benzaldehyde.

4. The process of claim 1 in which the aldehyde is alpha-naphthaldehyde.

5. The process of claim 1 in which the aldehyde is betanaphthaldehyde.

6. The process of claim 1 in which the pH of said aqueous solution is not greater than 4.

7. The process of claim 6 in which the aldehyde is present in the aqueous solution in a concentration of 10- to 10 moles per liter.

is made of carbon steel.

8. The process of claim 1 in which the metallic vessel 9. The process of claim 1 in which an inert atmosphere is maintained in said system.

References Cited 5 UNITED STATES PATENTS 10/1959 Hill 20847 6/1967 Godar 20848 OTHER REFERENCES Kirk-Othmer: Encyclopedia of C.T., Second Edition, vol. 6, p. 320 (1965).

DELBERT E. GANTZ, Primary Examiner.

G. E. SCHMITKONS, Assistant Examiner.

US. Cl. X.R. 252-146, 148 

